Pile resistor



March 10, 1942., l w, H. SMI-VH 2,276,069

PILE RESISTR Filed Sept. '7, 1940 JUETNESSESz lNVENTOR fk/'M414 f mzlwf/.5mm

Patented Mar. 10, 1942 PILE RESISTOR Walter H. Smith, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Eittsburgh, Pa., a corporation of Pennsylvania Application September 7, 1940, Serial No. 355,788

4 Claims.

This invention relates to resistors of the carbon pile' type.

Pile resistors are well known and have been utilized in regulating apparatus and systems for a number of years. The known pile resistors, however, were formed of a plurality of discs of resistance material, such as carbon or the like, supported by insulated rods which touched the edge of the discs of high resistance material or ed throughout the assembly nor is heat developed evenly therein, but instead a larger voltage drop is encountered at the end of the assembly where pressure is applied and released.

In a copending application of C. C. Whitaker, Serial No. 355,802, led September 7, 1940, there is disclosed and claimed a pile resistor in which the discs lof resistance material are supported on an insulating member to which a positive force is applied when pressure is released for effecting a positive movement of the insulating member through the stacked discs for obtaining an even separation of the discs when pressure is released. The pile resistor of C. C. Whitaker is effective for accomplishing the desired object of effecting an even separation of the discs when the resistor is employed as a regulator for load regulation.

However, it has been found that where such a resistor is employed as a part of a voltage regulating apparatus, that it is not sensitive enough for obtaining the desired Voltage regulation, since a change in the voltage which it is desired to regulate ci only a few volts, will not provide the force necessary for eecting the desired even separation of the discs.

It is an object of this invention to provide a pile resistor, the discs of which are disposed to be evenly positioned when pressure is applied or released to provide a uniform resistance throughout the unit, and give a resistor which is sensitive to small differentials in voltage when the resistor is employed as a part of a voltage regulator.

Another object of this invention is to provide a pile resistor in which the discs of the pile are carried by an insulating member which is supported in a substantially frictionless manner, and

a positive means separate from the pressure applying means and the stack of discs for effecting a positive movement of the insulating member throughout the stack to secure an even separation of the discs when pressure is released.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Figure l is an elevational View, partly in section, of a resistor embodying the teachings of this invention;

Fig. 2 is an elevational view, partly in section, of an embodiment of this invention;

Fig. 3 is an elevational View, partly in section, of a resistor illustrating another embodiment of this invention.

Fig. 4 is a fragmentary view, partly in section, cf the resistor of Fig. 2 modified in accordance with the teachings of this invention;

Fig. 5 is a fragmentary view, partly in section, of the resistor of Fig. 3 modified in the same manner as the resistor of Fig. 4; and

Fig. 6 is a diagrammatic view of a circuit in which the resistor of Fig. 1 is utilized.

Referring to Fig. 1, this invention is illustrated by reference to a resistor element I0 formed of a plurality of discs I2 of resistance material, such as carbon or the like. Any predetermined number of discs I2 may be utilized, depending upon the resistance value which it is desired to secure in the assembly. In the particular embodiment illustrated, the discs I2 are of the circular type having a predetermined thickness and having openings' centrally positioned therein so `that when the discs are stacked, as illustrated,

the openings are aligned.

In order to support the discs I2 in their aligned relation, an insulating supporting member is so disposed as to extend through the aligned openings of the discs. This insulating supporting member comprises a metallic rod lll having metal sleeves I6 disposed thereon and attached thereto as by means of the pins I8 and a tube of insulating material 2i) which extends between the sleeves I6. The discs I2 are in direct contact with the tube 2i) of insulating material, such as porcelain, Micalex, Pyrex glass, or the like, the weight of the discs at least causing Contact between the discs and the tubular member 20 along the upper edge of the tube 20. In all cases, the insulating tubular member 2D extends beyond the ends of the stacked and aligned discs I2l In order to retain the discs l2 in assembled position on the tube 20 of insulating material, a

fixed stop or end plate 22 is disposed at one end of the stacked discs I2 and is secured in any well known manner to a panel (not shown). The fixed stop 22 has an opening therein of a size suitable for permitting movement of the insulating tube 22 therethrough, as will be explained more fully hereinafter. Adjacent the other end of the stacked discs I2, a pressure plate or disc 26 is positioned to bear against the face of the end of the discs i2, the pressure plate being provided with a projecting end cap 23 which has a recess therein for receiving one of the sleeves I6 and the end of the tubulaimember 22. The end cap 28 is also provided with an opening through which the metallic rod I4 extends in a direction away from the pressure plate and the stacked aligned discs. The pin I3, which is utilized for holding the sleeve it in position with respect to the metal rod I4, may also be utilized for securing the end cap 25 in position with respect to the end of the insulating member 22 and stacked discs I2.

As illustrated, the xed plate 22 supports the one end of the insulating member 2l), the opening 24 in the fixed plate 22 being of sufcient size to permit longitudinal movement of the insulating member therethrough when pressure is applied or released. In order to support the other end of the metallic rod I4 which carries the insulating member 22, a bracket or flange plate 3l] is provided on the panel (not shown) the plate having an opening 32 therein through which the end of the metallic rod I4 projects. As illustrated, the opening 32 is also of sufficient size to permit longitudinal movement of the metallic rod I4 therethrough when pressure is applied or released. A spring member 34 is provided about the end of the metallic rod I4 and is held in position with respect to the rod and biased against the plate 30 by means of a cap 36 which engages the end of the spring 34. The cap 33 may be threaded onto the end of the rod I4 and is disposed to be adjusted for varying the tension of the spring 34, the purpose of which will be explained more fully hereinafter.

In order to apply pressure to the assembled discs, any suitable means can be employed such as the bell crank lever 38 formed by the short arm 49 and the long arm 42. The bell crank lever is disposed for movement about a pivot 44 in response to either the bias of a spring 46 which is secured between a fixed point 48 on the panel (not shown) and a projecting lug 53 of the bell crank 38 or in response to a force applied to the end of the long arm 42, as will be hereinafter described. The end of the short arm 4) which is disposed to bear against the end of the end cap 28 may be of any desired form so long as it does not interfere with the movement of the metallic rod I4. Thus, the end of the short arm 40 may be either a fork or may merely have an enlarged opening therein through which the rod I4 is disposed for unrestricted movement.

With the metallic rod I4 and the tubular member 2l] carried thereby secured to the end cap 28 of the pressure disc 26, when pressure is applied to the end cap 28 as by means of the spring 46, the discs are compressed, being forced to the right, as illustrated, against the xed stop or end plate 22, and simultaneously with the compression of the discs I2, the tubular member 22 of insulating material is moved longitudinally through the central openings of the discs relative to the discs. As will be apparent, since the tubular member 2D is free to move through the fixed 75 stop or end plate 22 and the plate 30, and since the ixed stop 22 limits the movement of the discs I2, a large movement between the discs I2 and the tubular member 20 will be obtained adjacent the xed stop 22, the relative movement between the discs I2 and the tubular member 20 progressively increasing from the end of the stack adjacent the pressure disc 26 until it reaches a maximum adjacent the xed stop 22. At the same time, the movement of the insulating member 20 and metallic rod I4 towards the xed plate 22 effects a compression of the spring 34 so that it will be biased to eect a movement of the metallic rod I 4 away from the xed stop 22 when the pressure is released.

With the discs under pressure, as described hereinbefore, when the pressure is removed from the end cap 2B, it is found that the spring member 34 effects a positive movement of the rod I4 and insulating member 20 away from the xed stop 22 throughout the stacked discs I2, and that the frictional resistance between the discs I2 and the tubular member 20 cooperates with the positive movement of the insulating member 22 to effect a movement of the discs I2 adjacent the xed stop 22 at the same time that the discs adjacent the pressure disc 26 move as a result of the release of the compressive force on the assembled disc. The amount of the positive movement of the insulating member 2D through the stack of discs I2 will depend upon the amount of pressure released, since, in all cases, the spring 34 is adjusted in a predetermined manner to so cooperate with the pressure applying means that, as the pressure is released, the spring will insure a movement of the rod I4 away from the fixed stop 22 in an amount just equal to the movement towards the xed stop when an equal amount of pressure is applied.

In addition to effecting a movement of the discs I2, it is found that the positive movement of the tubular member 20 relative to the discs when the pressure is released, effectively breaks up any static friction between the discs and the tubular member. As will be understood, the frictional resistance between the discs and the tubular member 2i) of insulating material will be a maximum adjacent the fixed stop 22, and will be progressively decreased in the direction of the pressure disc 22, since the relative movement of the tubular member 2i! with respect to the discs I2 when pressure is released progressively decreases from the fixed stop 22 in the direction of and to the pressure disc 26.

In the embodiment illustrated in Fig` l, the weight of the assembly is carried by the plates 22 and 32. In some cases, it is found that the friction encountered in carrying the stacked assembly in the plates 22 and 30 is detrimental where it is desired to provide a very sensitive and uniform operation of the resistor. In order to provide a resistor which is sensitive and responsive to very small changes in voltage, it is desired to support the insulating member 20 which carries the assembled discs in a substantially frictionless manner with respect to the plates 22 and 3U so that the insulating member 20 is relatively free moving with respect to the supporting plates when pressure is applied or released.

In the embodiment illustrated in Fig. 2, the metal rod I4 and the insulating member 2B project through enlarged epenings 24 and 32 in the plates 22 and 30, respectively, in a frictionless manner, the plates 22 and Si! being employed for the purpose of guiding the rod I4 when it is moved. In this embodiment the Iplate 22 carries a bracket 52, the bracket 52 being secured thereto in any suitable manner. At the end of the bracket 52 one end of a leaf spring member 54 is secured as by means of the screws 5B, the leaf Spring 54 being disposed to extend downwardly in the path of -movement of the rod I4. As illustrated, the rod I4 has its end machined to provide a shoulder, the small end of the rod I4 projecting through a suitable opening in the end of the leaf spring 54 and being carried thereby. As will be understood other means such as cotter lpins extending through the rod I4 may be employed in place of the machined shoulder. rPhe leaf spring 54 may be of any desired strength, depending upon the amount of force which is to be applied to the assembly.

At the other end of the stacked discs, the plate 30 carries a fiange 58, at the end of which is pivotally hung a link 60 which is provided with an opening 62 through wihch the rod I4 -projects, the rod seating on the lower surface of the opening and being supported by the link. As illustrated in Fig. 2, the force may be applied to the link 60, as by means of the bell crank 38 in a manner similar to that illustrated in Fig. 1. Since the link 8B is pivotally carried by the flange 53, it is apparent that this support is substantially frictionless with respect to the plate 32.

With the metallic rod I4 carried by the link v 60 and the leaf spring 54, the rod I4 and insulating member 22 are relatively free moving with respect to the plates 22 and 38. Further, since the leaf spring 54 opposes the application of force to the insulating member, it is quite apparent that any force which has been applied is released, a positive movement of the rod I4 and insulating member 20 in a direction away from the xed stop 22 is secured in a substantially frictionless lmanner with respect to the plates 22 and 3U throughout the stack of discs i2 to effect a substantially even separation of the discs. The positive movement insured by the use of the leaf spring 54 is sufficient to effect a movement of the insulating rod 20 throughout the stack in a direction away from the xed stop 22 in an amount equal to the movement of the insulating rod in a direction toward the fixed stop 22 when an equal amount of pressure is applied.

Referring to Fig. 3 of the drawing, another embodiment of this invention is illustrated. In this embodiment, the metallic rod I4 and insulating member 2li carrying the assembly of the discs I2 are supported in a substantially frictionless manner with respect to the plates 22 and 3B by means of two leaf springs 54 and 64, respectively. As illustrated, the support for carrying the leaf spring 54 is the same as outlined in the embodiment of the invention illustrated in Fig. 2. The support for leaf spring 64 is similar to the support for leaf spring 54, being formed by a bracket 66 secured to the plate 3U, one end of the leaf spring 54 being, in turn, secured to the bracket 66, while the other end is provided with a small opening through which the metallic rod I4 projects. As illustrated, the projecting end of the metallic rod I4 to the left of the leaf spring 64 is provided with a shoulder for abutting the leaf spring 64,'so that as the metallic rod I4 is moved in a direction towards the fixed stop 22, both of the leaf springs 54 and E4 are forced to the right and tend to bias the metallic rod I4 and insulating tubular member 20 carried thereby in a direction away from the fixed stop 22.

In the embodiment illustrated in Fig. 3, the leaf springs 54 and 64 support the metallic rod I4 and assembly carried thereby in va substantially frictionless `manner with respect to the plates 22 and 30, and also provide a positive force for effecting a positive movement of the insulating member 2Q throughout the stack of discs when pressure is released.

As illustrated in each of Figs. 4 and 5, the coil spring 34 of Fig. l may be utilized with the structures of Figs. 2 and 3. The use of the coil spring and the adjustable nut 36 with the particular structures of Figs. 2 and 3 is of advantage where the spring members 54 and 64 are not very strong but are used primarily for supporting the metallic rod I4 and the assembly carried thereby in a substantially frictionless manner with respect to the plates 22 and 30. Further, the tension of spring 34 can readily be adjusted so that when embodied in either of the structures illustrated in Figs. 2 and 3, a finer degree of adjustment can be obtained and the apparatus of Figs. 2 and 4 can be more widely employed in industry where the pressures encountered will vary to a considerable extent. In all of the structures of Figs. 2 through 5, the metallic rod I4 and the assembly carried thereby are supported in a substantially frictionless manner with respect to the plates 22 and 30, and a positive drive, which is separate from the `pressure applying means and from the stacked discs, is provided for insuring a positive movement of the insulating member throughout the discs for obtaining an even separation of the discs when pressure is released.

Referring to Fig. 6, the resistor I0 of Fig. 1 is illustrated as employed in a voltage regulating system for regulating the voltage generated from a generator 68. The armature 'III of the generator is illustrated as being connected by conductors 'I2 and 'I4 to a load It. A switch 'I8 is provided in the load circuit for closing the circuit through the load it. A shunt field winding S9 of the generator 68 is illustrated as connected in shunt -circuit relation with the armature 'I0 between the conductors 'I2 and '14. The resistor element I of this invention is connected in series with the shunt neld winding between the conductors 'I2 and '14. Since it is desired to control the voltage generated iby the generator 68, an electromagnetic coil 82 is also disposed to be connected between the conductors 'I2 and 'I4 so that the voltage across the winding 82 is indicative of the voltage across the load 16.

As illustrated, the bell crank 33 employed as the pressure applying means for the pile resistor I0 is mechanically connected at the end of its long arm to an arm 84, one end of which carries an iron or magnetic portion 86 disposed to be actuated by the energization of the coil 82. When energized, the coil 82 tends to lift the iron or magnetic core portion 86, thereby rotating the bell crank 38 in a counterclockwise direction against the bias of the spring 46 to decrease the pressure applied to the stacked discs, thereby increasing the resistance in circuit with the field winding 80.

In operation with the switch 'Iii closed and the tension of the springs 34 and 36 adjusted in a predetermined manner, so that with normal or a predetermined voltage across conductors 'I2 and 14, a predetermined pressure is applied to the resistor element I0 for maintaining a predetermined amount of resistance in the shunt fleld circuit. If for any reason the voltage generated by the armature lll fluctuates from this predetermined normal value of generated voltage, as, for example, if the voltage generated increases above the predetermined value, the coil 82 will become sufficiently energized to overcome the pull of the spring fii to cause the bell crank 33 to rotate in a counterclockwise direction about its pivot to release some of the pressure from the stacked discs I 2. As the bell crank 38 rotates to release the pressure on the stacked discs, the spring member 3ft functions to eflect a positive movement of the insulating member throughout the discs in a direction away from lthe xed stop 22. The frictional resistance between the discs of the assembly and the tubular insulating member, as the tubular insulating member is moved through the stack away from the stop 22, effects an even separation of the discs, giving a substantially uniform voltage drop across the stacked discs. The amount of the movement of the insulating member, as effected by the action of the spring 34 when the pressure is released, is equal to the movement of the insulating member in the opposite direction when an equal amount of pressure is applied to the stacked assembly. This increase in the resistance introduced in circuit with the field winding dil reduces the excitation of the coil S2 so that the resulting generated voltage is decreased.

If, however, the voltage generated is decreased from the normal generator voltage value, the pull of the spring t3 effects a movement of the bell crank 33 in a clockwise direction about its pivot, whereby more pressure is applied to the carbo-n disc assembly, thereby decreasing the resistance in circuit with the shunt field winding 8@ to increase the generator voltage.

Where the resistor element of this invention is employed, either for the purpose of load regulation for voltage regulation as described, a very close control is Obtained. This is especially true where the resistor element is utilized in voltage regulating systems where regulation must be provided for maintaining very small differentials of voltage of the order of less than two volts, it being found that in a system as illustrated in Fig. 6 that the element is suflieiently sensitive to maintain the voltage generated substantially constant with a permissible variation of only two volts. This close control is obtained only where a positive drive for the insulating member carrying the discs l2 is provided which is separate from the pressure applying means. supporting of the metallic rod and insulating member, as described hereinbefore, cooperates with the positive drive for providing an extremely sensitive regulating apparatus.

By employing the resistor element of this invention, it is found that the desired results can also be obtained with a small disc assembly, since fewer discs of the high resistance material are necessary for obtaining the desired voltage drop in the element where the positive drive is employed, the construction described eiectively breaking up the static friction in a uniform manner between all of the discs in the assembly and providing for a uniform heating of the assembled discs in service.

Although this invention has been described with reference to a particular embodiment thereof, it is, of course, understood that the invention is described as illustrative only and is not to be interpreted in a limiting sense.

'The frictionless y I claim as my invention:

1. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending through the central openings to support the discs in stacked alignment, a stop disposed at one end of the aligned discs, means for applying pressure disposed at the other end of the aligned discs for applying pressure to the discs and moving the insulating member longitudinally through the stack, and a spring means separate from the pressure applying means disposed for effecting a positive movement of the insulating support member in a direction away from the stop, the frictional resistance between the discs and the insulating member as the insulating member moves therethrough effecting an even separation of the discs throughout the stack when pressure is released.

2. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending through the central openings to support the discs in stacked alignment, a stop disposed at one end or" the aligned discs, means for applying pressure disposed at the other end of the aligned discs for applying pressure to the discs and moving the insulating member longitudinally through the stack, and a support member disposed adjacent each end of the aligned discs for carrying the insulating member in a substantially frictionless and relatively iree moving manner with respect to the stop, one of the support members comprisinor a leaf spring member disposed for effecting a positive movement of the insulating member in a direction away from the stop when the pressure is released, the irictional resistance between the discs and the insulating member cooperating with the positive movement oi the insulating member to effect an even separation of the discs throughout the stack when pressure is released.

8. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending through the central openings to support the discs in stacked alignment, a stop disposed at one end of the aligned discs, means for applying pressure disposed at the other end of the aligned discs for applying pressure to the discs and moving the insulating member longitudinally through the stack, means for supporting and carrying the insulating member in a substantially irictionless manner for rendering it relatively iree moving with respect to the stop when pressure is applied and released, and a spring means separate from the pressure applying means disposed for effecting a positive movement of the insulating member in a direction away from the stop whereby the frictional resistance between the discs and the insulating member as the insulating member moves therethrough effects an even separation of the discs throughout the stack when pressure is released.

4. A pile resistor comprising, a plurality of discs of resistance material having central openings therein, an insulating member extending 'through the central openings to support the discs in stacked alignment, brackets disposed at opposite ends of the stack and having openings therein for receiving the ends of the insulating member to guide it when moved, a stop associated with one of the brackets for limiting the movement of the stack in a direction towards the stop, a leaf spring member associated with each of the movement of the insulating support member in a direction away from the stop When the pressure is released, the frictional resistance between the discs and the insulating member cooperating with the positive mweinent of the insulating member to eiect an even separation of the discs through-- out the stack when pressure is released.

WALTER H. SMITH. 

